Before that, I believe there was a command in TclX from which clock was derived. You could look around for an old version of TclX to match your old version of Tcl and try your luck, I guess.

Unfortunately this is for the editor Alpha which is stuck with Tcl 7.4 (more or less) and no 'load' command. We are working on a newer 8.3.x release for Alpha, but that's not stable enough to unleash yet, BUT I'd like to write code which uses 'clock' and will work in that old version of Alpha as well --- the ideal demand for something like forwards compatibility! Anyway, I took the plunge and: